Effects of Estradiol on Prolactin Production and Dihydroergocryptine-Induced Inhibition of Prolactin Production in Primary Cultures of Rat Pituitary Cells*

Abstract

We have used primary cultures of male rat anterior pituitary cells to characterize two effects of pretreatment with 17β-estradiol: 1) the ability to overcome the inhibition of PRL accumulation in the medium (production) by dihydroergocryptine, a dopamine agonist, and 2) the stimulation of PRL production. Medium containing untreated serum contained 20 pm estradiol (E₂). In this medium, incubation with dihydroergocryptine for 12 or 24 h caused half-maximal inhibition of PRL production at 150 pm; maximal inhibition reduced values to 32% of the control value. Pretreatment with 50 nm E₂ for 5 days decreased the maximal inhibition of PRL production caused by dihydroergocryptine to 65% of control values, with little or no effect on the concentration of ergot which caused half-maximal inhibition. In addition, pretreatment with 50 nm E₂ did not increase basal PRL production. Medium containing charcoaltreated serum was calculated to contain less than 2 pm E₂. In this medium, dihydroergocryptine caused half-maximal inhibition of PRL production at 30 pm; maximal inhibition was reduced to 32% of controls. E₂ decreased the maximal inhibition of PRL production to 60% of controls and caused an increase in the halfmaximal concentration of dihydroergocryptine which ranged between 7- and 32-fold, with an average of 18-fold. With most batches of treated serum, but not all, E₂ stimulated basal PRL production 1.6- to 5.9-fold. The E₂ effect on the response to dihydroergocryptine was maximal at 2 days; the E₂ effect on basal PRL production was still increasing between 2–5 days of exposure. Both effects were maximal at 50 pm E₂. Diethylstilbestrol (5 nm) showed the same effects as E₂) but 50 nm progesterone, testosterone, or hydrocortisone did not. Therefore, even though both effects of E₂ do not necessarily occur together, both effects are pharmacologically specific and occur at similar doses and times after pretreatment. (Endocrinology106: 1108, 1980)